How to Fix Sagging Floor Joists

The 2nd story floor on one side of our 1940s lake house renovation had a noticeable low spot in the middle of it. This was due to cracked and sagging floor joists that were exposed when we demoed the interior. While some of the joists were just sagging due to a weak floor system in general, some had holes too close to the edge or a big knot that caused a crack and really weakened the joist, putting even more pressure on the surrounding floor joists. To fix this we needed to sister new joist to the old joist to stiffen and flatten the floor.

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[southernrrman]

My brother-in-law did it wrong like you did, beating the new joist into place. He sistered every joist on his old house. Beating those joists in - something has to move. In his case it popped his subfloor loose which ruined the hardwood finish flooring. He had to remove (and trash) the finished floor, reattach the sub, then install new hardwood. Best to bevel those edges or rip a little off. Also construction glue is a good idea here.

[squantrill]

Thank you, I needed to understand what was involved as we recently moved into a house where the surveyor missed a sagging undulating floor idiotially. Now we are getting quotes on the work involved and knowing what is involved really helps.

[peep]

I had to do a lot of this in my house, but I didn't have nearly the access you did. So since I already had the outside wall apart, I just slid the sisters in from the outside. I prefer to jack the old joists up so they're proud an 1/8th to a 1/4 in the center span before I glue and screw the sister. It flattens back out a lot once you release the jacks. And more over time, especially with load. My house was a real basket case though, including a carrying beam that was about an inch and a half low compared to the foundation

[rkerby]

You did an Amazing job sistering joists to the existing floor joists.
Well done!

[joewreckingballbiden]

Put about a 3/8 to 1/2 in bevel on the top of the joist so it bangs in easier, Joist is 1 1/2 "so you still have 1'' at the very top. can also do that on the opposite side on the bottom just where the bearing is. Joist is just as strong with those bevels. Don't do it all the way across on the bottom, just the top. Lean the joist in at the top to the one being sistered with the bevel facing out on the top, bang the bottom in. Even wax on the bottom ends will help it slide in easier.

[cejkwo]

Should of used construction adhesive between the old and new

[stevenshorten]

Wouldn't the crown of the old joist start to add pressure on the new joist a little bit?

[michaelbell]

Every time he says joist, drink.

Me 30 seconds in…hammered! 😂

[mikeking]

2x8 joists 24 OC? And crappy wood? I would have glued and screwed them and added two rows of blocking.

[questioner]

Now that the floor is stronger, have you considered using it to lift the house? You could have a higher ceiling down there!

[allen]

Don't most people drill a tight hole and run bolts through to sister ? Iv never saw anyone nail them .

[erniegu]

Thanks for the great video, I'm planning to do the same but wonder how folks think if this would cause issues when the house is being sold

[richardhullfish]

Should have nailed the old joist to the new joist also. Nail on both sides of the joist's. When you scab a joist I always nail both sides. Nice job.

[lols]

You mentioned that 2 x 8 joists should support max 12 feet span. What is the max for 2 x 10 joists ?

[jdodport]

What was the process of jacking up the joists? Jack one joist at a time until level? Start in the center of the room? Please explain.

[chuckyy]

Joist must be a smaller profile than original, how can he just slide in and push into place?

[jeffyoder]

This is kind of the opposite of my problem. We have a bow window and fireplace that are cantilevered out beyond the basement wall below. The cantilever joists were not made long enough so they are bowing the floor up due to the weight of the wall and roof pushing down on the outer end of them. Not sure how to correct that without cracking drywall and relaying the laminate in that room since it has a metric $h!t ton of leveling compound under it.

[ShowStoppersvSoccerTour]

You didn't show the one part i was interested in. How did you tilt the sister joist up flat to the original joist? The diagonal of the 2x8 is greater than the distance between the floor above and the sill plate and i-beam.

[lungshentsao]

structural engineer here. whoever put a hole right in the mid span of a 2x joist is an idiot :/ that joist looks like it is about to break in half if you haven't take any action to fix it.

[vanstromi]

Honestly, these videos are frustrating. Speed through all the good stuff, don’t include much detail and use an example where you don’t run into any issues, obstacles etcetera. I have a cracked floor joist above my furnace in a tight space. I have one in my ceiling between my garage and my master bedroom with not enough room to slide in a 2x10 the length of the existing joist. What do I do? I mean, I know what to do for a full length floor joist. That’s easy.